The present invention refers to a rolling stand, and in particular to a coating unit with a stationary roll and at least one movable roll whose roll necks are supported in a bearing unit which cooperates with a control mechanism for radially displacing the movable roll relative to the stationary roll and thus for adjusting the gap therebetween.
The manufacture and refining of foils or webs by means of rolling mills e.g. for rolling of metal foils and plastic foils, coating of foils and strips by using calender or coating units rolls, frequently demands that the spacing between the rolls and thus the gap width be accurately maintained to attain a uniform product of equal thickness. In addition, economical reasons require during rolling operation and in particular during application of expensive coatings to operate at the lower tolerance limit of the guaranteed thickness so as to save material.
To meet these demands, the use of highly sophisticated control mechanisms were proposed in order to compensate non-circular or eccentric rolls during running of the latter in addition to precise and expensive bearings for the journals of the rolls. Such bearings were considered necessary as even a small bearing play should be avoided in the event the foil or solvent advancing through the roller gap exerts only relatively small reaction forces as this is the case during production of plastic foils or coating foils with the aid of a (third) doctor roll, so that the solvent e.g. for carbon film, is pre-metered by the doctor and contra-rotating rolls. Especially when treating solvents without foils of small thickness and thus requiring small gap widths, the demand o relatively high accuracy with deviations of less than 1 micrometer reaches the limits of providing suitable bearings.
There are known rolling mills in which the housing is mechanically or hydraulically prestressed e.g. by interposing pressure elements or hydraulic cylinders between the roll chocks, in order to compensate changes of the gap width which are caused through load variations in the roller gap. However, this method for prestressing the housing as used for metal rolling mills is not suitable for coating units because there are practically no reactions forces exerted thereon. Apart from that, this prestressing method for the housing is still not able to maintain the accuracy of the gap width between the rolls.